²⁹ The next day he saw Jesus coming toward him and said, “Behold, the Lamb of God, who takes away the sin of the world. ³⁰  He is the one of whom I said, ‘A man is coming after me who ranks ahead of me because he existed before me.’ ³¹ I did not know him, but the reason why I came baptizing with water was that he might be made known to Israel.” ³² John testified further, saying, “I saw the Spirit come down like a dove from the sky and remain upon him. ³³ I did not know him, but the one who sent me to baptize with water told me, ‘On whomever you see the Spirit come down and remain, he is the one who will baptize with the holy Spirit.’ ³⁴  Now I have seen and testified that he is the Son of God.” (John 1:29-34)

After John’s interrogation by priests, Levites and Pharisees, the evangelist proclaims Jesus as “the Lamb of God, who takes away the sin of the world!’ This is but the start of a short, compact testimony by the Baptist witnessing to the One he had just baptized.

• “Behold the Lamb of God… (1:29)
• who takes away the sin of the world.” (1:29) 
• The one who existed before John (1:30-31) 
• The one on whom the Spirit came from the sky and remain upon him (1:32-33) 
• “he is the Son of God.” (1:34) 

The Fourth Gospel does not record, as the Synoptic Gospels do, the baptism of Jesus by John. However, the coming of Jesus mentioned in this verse was not his coming for baptism, because, as the reading implies, John had already witnessed the descent of the Spirit upon Jesus when he had baptized him. John already knew who Jesus was, and therefore said to those around, “Behold, the Lamb of God, who takes away the sin of the world”